The invention resides in an injection molding nozzle including an elongated base body through which a channel extends for conducting a melt through the nozzle and on which an elongated temperature control element is arranged including a heating element for supplying heat to the base body and which includes heating coils at the two ends of the temperature control element.
Such an injection molding nozzle has been built by the assignee and sold for many years. In the known injection molding nozzle a heating element is disposed on a sleeve which can be slipped onto a generally cylindrical base body. By means of the heating coil, the base body of the injection molding nozzle can be heated so that the melt flowing through the channel remains liquid.
Since the base body of the injection molding nozzle is at its end areas always connected to an injection molding tool, heat is conducted out of the end areas of the injection molding nozzle into the injection molding tool whereby the end areas of the injection molding nozzle are cooled down. This is very disadvantageous since in those end areas the melt can solidify so that it can no longer be worked.
Furthermore, since in the center area of the base body, no heat loss occurs the temperature in this area may become excessively high. This is also disadvantageous since it is very important for the quality of the melt and consequently for the product to be manufactured that the temperature of the melt along the channel is as uniform as possible.
In order to overcome these disadvantages, the injection molding nozzles are provided at their connecting locations with the tool with a heat insulating element as for example a ceramic ring, as it is known for example from DE 10 2004 009 806 B3. Another possibility resides in providing a heating coil which is tighter wound in the end areas of the base body than in its center area. In this way, the end areas of the base body of the injection molding nozzle are heated to a greater degree than the center area.
From DE 20 2009 011 904 U1 for example a heating element is known which includes a sleeve on which a heating coil is disposed. The windings of the heating coil have a very low pitch in the end areas of the sleeve but a very high pitch in the center area of the sleeve. In this way, there are fewer windings in the center area than in the end areas whereby the center area of the sleeve is heated to a lesser degree than the end areas of the sleeve.
Although with the known measures that the heat loss of the two ends of the base body of injection molding nozzle is reduced or, respectively, the two ends are heated to a greater degree than the center area of the base body of the injection molding nozzle, it still can happen that, because of a heat backup, the temperature in the center area of the base body of the injection molding nozzle reaches values at which the melt in the channel can be damaged. The temperature distribution over the length of the channel is therefore still not satisfactory.
It is the object of the present invention to provide an injection molding nozzle of the type described above wherein the temperature distribution of the melt in the channel is improved.